This invention relates to a valve for controlling or blocking the flow of fluid between two ports using a stretchable diaphragm and employing an actuating device that is capable of amplifying external forces to aid in the stretching of said diaphragm and to overcome internal fluid pressures.
Valves of this type are used for corrosive, erosive, and also sanitary applications where there must be no hidden cavity that may harbor bacteria or other impurities. Furthermore, valve parts wetted by such critical fluids must be made from highly polished metal requiring easy accessability of such metal parts. A prior art valve used for such service is U.S. Pat. No. 4,813,648 in which an elastomeric seal is placed around the circumference of a movable metallic plug or piston in order to block fluid flow between two coaxial ports. However, such a design is not permissible for certain biotechnical applications since it offers narrow cavities between the sliding interfaces of the piston and valve housing. Such narrow cavities are very difficult to sterilize and would require the frequent disassembly of such a valve for cleaning purposes. My invention overcomes these difficulties by placing the moveable piston behind a stretchable diaphragm, thereby, providing absolutely no cavities within the wetted valve portion.
Other prior art valves of this type offer valve cavities that are nearly identical in cross-sectional shape to my invention, however, their diaphragm design is molded to roll into the receptive, sealing body cavity (See FIG. 4 of my application). Such rolling diaphragms require precision tooling for molding purposes, which would also be expensive if one considers the number of different types of elastomers that might have to be made depending on the type of service application. Finally, any convoluted portion protruding out of the original body cavity might hinder the drainage and enhance the entrapment of impurities of the valve. In my invention, the diaphragm can be cut from any available sheet stock. Furthermore, by stretching the diaphragm, there will be no slackened portion forming undesirable cavities when the valve is open in contrast to said prior convoluted art diaphragms.
Lastly, the diaphragm in my invention has a built in retention force which enables it to assume its original shape, thereby, overcoming the suction effects if the valve is handling a fluid in the state of vacuum. No mechanical attachment of my diaphragm is therefore required in contrast to prior molded art diaphragms which do require a mechanical coupling for their respective pistons or stems (See FIG. 4).
The degree of tension within the diaphragm is, besides the mechanical stress limitation of the selected elastomer, a function of the cone angle. If the cone angle (included angle of chamber 6) is very large, than there is little stretching (strain) of the elastomer, i.e. very little tension in the material that would tend to restore the elastomer to its original flat shape. If the angle is too small, then the internal stress resulting from the stretching will exceed the yield point, and the elastomer will remain permanently deformed. I have found that a cone angle of between 70 and 100 degrees gives the best results in staying within the elastic limits of most elastomers while providing enough "restoration" stress to resist a full vacuum pressure differential to separate the diaphragm from the outer surface of conical element 12.
For sterilization purposes, it is desirable that the housing and mechanism be of low mass and have no air pockets, which is again very easily achieved in my invention. Another requirement is that these valves should be able to be actuated by air yet be very compact. I offer for this reason an amplifying mechanism that is capable of multiplying the forces of a relatively small air cylinder which will thus be able to overcome not only the stretching resistance of the sealing diaphragm, but also the opposing hydrostatic fluid forces. A further improvement of my invention is in the retention of the diaphragm, which not only concentrates the clamping forces against the housing at the point of the most likely entrance of contaminants, but also allows an escape area for that portion of the clamped diaphragm which sees swelling due to the heating action of sterilizing steam.
These and other objectives of my invention will be more easily understood from the following descriptions and annexed drawings: